Need help finding short for electrical ground

[aolitesnsirens]

Hey guys, I've got a 1977 Chevy K10 Cheyenne Stepside that I've had for about 25 years. Just getting around to putting it back together since I'm newly retired and have time to finish it. I painted the chassis a while ago and just recently put the bed back on. I'm putting the cab back together and I've got an issue now with the electrical. Everytime I step on the brake pedal, the dash lights come on. I figured the rear taillights might not have a good ground, so I cleaned the bolts holding the bed to the frame and that didn't solve the issue. I've since bought a grounding strap and attached that to the ground for the taillights, but that only solved part of the issue, (just the turn signal lights come on when brake pedal is pressed). I'm tapped out and need some help what to look for next. Any help would be greatly appreciated.

 

[Matt69olds]

What are the odds the taillights come on when this happens? Lay a brick on the brake pedal, walk around the truck.

Check all the bulbs. Make sure you don’t have a single filament bulb where a dual filament dual filament should be. This is actually a fairly common problem.

At the rear of the truck, the green or yellow are Left/right turn signal or brake brake light wires, the brown wire is taillights. If you have a single filament bulb, the center pin can jumper across both terminals at the base of the bulb socket. If that happens, power than normally turns on the brake lights will power the taillights thru the brown wire. Since the dash lights get power from the taillight circuit, they also light up.

That’s my theory.

 

[PrairieDrifter]

Check all bulbs, then there should be a ground on I think the passenger side behind the tail light housing that on the earlier trucks just jumps to the passenger side, the later trucks had ground lugs on both sides.

 

[aolitesnsirens]

What are the odds the taillights come on when this happens? Lay a brick on the brake pedal, walk around the truck.

Check all the bulbs. Make sure you don’t have a single filament bulb where a dual filament dual filament should be. This is actually a fairly common problem.

At the rear of the truck, the green or yellow are Left/right turn signal or brake brake light wires, the brown wire is taillights. If you have a single filament bulb, the center pin can jumper across both terminals at the base of the bulb socket. If that happens, power than normally turns on the brake lights will power the taillights thru the brown wire. Since the dash lights get power from the taillight circuit, they also light up.

That’s my theory.

ok thanks, I'll look at it tomorrow and let you know.

 

[aolitesnsirens]

Check all bulbs, then there should be a ground on I think the passenger side behind the tail light housing that on the earlier trucks just jumps to the passenger side, the later trucks had ground lugs on both sides.

Both taillights have ground lugs to the bed of the truck on my truck.

 

[aolitesnsirens]

ok thanks, I'll look at it tomorrow and let you know. In case I didn't make it clear, when I step on the brake pedal, everything on the instrument panel comes on and on the outside of the truck the front turn signals and rear brake lights come on as well. So my truck lights up every time I step on the brake pedal. I'll still check the bulbs and let you know.

 

[PrairieDrifter]

Both taillights have ground lugs to the bed of the truck on my truck.

77 could have been the year that it changed.

 

[Andronikos]

The dash lights are "finding" their own path to ground. I grounded everything to the frame. Using the ground straps like you did for the bed I grounded the bed to the frame, cab to frame, radiator core support to frame, and engine to frame at the same bellhousing bolt as the battery negative. You can never have too many grounds. Edit: I almost forgot the most important one - Fuel filler neck to frame.

 

[75gmck25]

Ground for the dash lights is a black wire connected to a post on the top of the emergency brake pedal, which then grounds by being bolted to the body. Symptoms sound like it is not connected, or you painted something that should have been left bare metal.

 

[Ricko1966]

Dash lights have a constant ground to the best of my knowledge so it wouldn't matter if they found their own path to ground or you added 97 paths to ground,if they are lighting when they shouldn't. They are getting power when they shouldn't. The power is most likely being back fed through another bulb in the truck,through the hazard switch or the turn signal switch.

 

[aolitesnsirens]

Ok, I've isolated it to something in the cab by disconnecting the electrical plug for the bed lights. I'm going to take apart the dash and see if I can try and find something behind the instrument cluster. Somehow it has to be in the cab.

 

[75gmck25]

Trust me - check the main dash ground first. If missing, it will definitely affect dash indicator lights and other functions. It’s a 10 second check to make by looking up under the dash, and may save you time later.

 

[aolitesnsirens]

Trust me - check the main dash ground first. If missing, it will definitely affect dash indicator lights and other functions. It’s a 10 second check to make by looking up under the dash, and may save you time later.

I've checked the main dash ground. It's good. Something else is backfeeding the dash lights. I can't figure it out. This is so frustrating because I know it's something simple.

 

[aolitesnsirens]

It's weird, if I put a ground strap on the fame and attach it to the ground wire for the rear taillights, the dash lights don't come on with the brake pedal pressed, just the turn signal lights come on in the cab. But with no ground strap, all instrument lights and turn signal lights come on when the brake pedal is pressed.

 

[PrairieDrifter]

Jiggle and depress the crap out of the hazard switch

And again check EVERY bulb

We're gonna check every single ground and make sure it has clean metal to make contact with.

There should be two ground locations on the core support, for both sides of the light harness, up on the top rail. The side by the battery should technically be attached to both the battery and frame by the rad.

The ground above the parking brake lever, you may have to remove the tab from the mount and clean under that.

The ground from the battery to the engine block. I tie mine in with the frame ground for good measure.

From the back of the passenger head to the firewall.

The tail light grounds.

I've never seen a factory bed to frame ground but it is a good idea.

The next step would be to jump the tail light grounds to a spot on the frame. Not factory, but a mod/test.